The present invention relates to lubricant compositions containing molybdenum compounds and antioxidants and methods of making them.
Molybdenum disulfide is a known lubricant additive. Unfortunately, it has certain known disadvantages some of which are caused by its insolubility in lubricating oils. Therefore, certain oil-soluble molybdenum sulfur-containing compounds have been proposed and investigated as lubricant additives. For example, U.S. Pat. No. 2,951,040 discloses an oil-soluble molybdic xanthate as useful in lubricating compositions. U.S. Pat. No. 3,419,589 discloses the use of certain xe2x80x9csulfurizedxe2x80x9d molybdenum (VI) dithiocarbamates as lubricant additives. These additives are described as being oil-soluble or at least capable of being easily suspended in oils. U.S. Pat. No. 3,840,463 discloses the use of certain metal dithiocarbamates or dithio-phosphates in combination with metal-free additives that contain sulfur and phosphorus. U.S. Pat. No. 4,966,719, U.S. Pat. No. 4,995,996, and U.S. Pat. No. 4,978,464 all relate to the preparation and use of molybdenum compounds.
U.S. Pat. No. 4,705,641 discloses the use of certain copper salts and molybdenum salts in a basestock as antioxidants and antiwear agents. Copper and molybdenum carboxylates are preferred. The uses or benefits of trinuclear molybdenum containing compounds are not disclosed, and, in fact, oil-soluble trinuclear molybdenum compounds were not known at the time of the invention disclosed in the foregoing patent.
Dinuclear molybdenum compounds known in the art are characterized by a different oxidation state (Mo(V)) from that of trinuclear containing molybdenum compounds (Mo(IV)) of the present invention. Thus, one skilled in the art would not be able to predict the behavior of these Mo(IV) compounds in lubricating oils from the behavior of the dinuclear compounds. More specifically, in view of the difference in oxidation state, the performance of such compounds in redox reactions typical of systems that contain lube oil additives would not be known or predictable given a knowledge of the performance of dinuclear molybdenum compounds in those systems.
U.S. Pat. No. 4,559,152 discloses oil soluble salts of organophosphorus acids prepared by reacting at least one organophosphorus acid in an inert solvent mixed with a polar solvent and an oxymolybdenm compound of certain formulas. However, oxymolybdenum compounds containing trinuclear molybdenum were not synthesized. U.S. Pat. No. 4,559,152 discloses only an elemental analysis of the products, and the ratios of elements disclosed does not, in itself, indicate the presence or teach the preparation of trinuclear oxymolybdenum compounds. In fact, the presence of excess alkyl dithiophosphate ligand reactants as contaminants in the reaction products or a mixture of mono-, di- and tetranuclear oxymolybdenum compounds as products could yield Mo and P ratios identical to those expected for trinuclear oxymolybdenum compounds, without producing them.
U.S. Pat. No. 4,846,983 discloses and claims metal oxygen (and optionally sulfur) core containing compositions in which the core contains at least one generally from 1 to 25 and the metal can be molybdenum. However, oxymolybdenum and oxosulfidomolybdenum compounds containing trinuclear molybdneum were not synthesized. The ""983 patent discloses a novel method for generating H2S, through the use of monoalkylthiocarbamates, which decompose upon heating and release H2S. The synthetic conditions in ""983 are similar to those disclosed in patents and known in the art to make mononuclear and dinuclear molybdenum thiocarbamates.
Trinuclear molybdenum compounds have been reported but they are either ionic or have ligands with short chain alkyl groups, see, e.g., Shibahara, Coord. Chem. Rev. 123, 73-148 (1993). The reported compounds are consequently not oil soluble, and they have not been reported as lubricating oil additives.
WO 95/07963 to Shaub teaches lubricating compositions of an aromatic amine of a specified formula and dinuclear molybdenum compounds of the general formula Mo2O2S2(dtc)2 and Mo2S4(dtc)2 (dtc means dithiocarbamates) have synergistic antioxidant properties. However, Shaub""s comparative example indicates that a different molybdenum compound Mo(S2)(dtc)3, does not exhibit such synergies with aromatic amines. The results indicates that a synergistic effect between any given molybdenum compounds and aromatic amines would not be predictable or expected. EP 94928344.4 discloses the use of diphenylamine antioxidant in combination with molybdenum.
There is a continuing need for additives that demonstrate enhanced lubricating properties, particularly friction reducing and/or anti-wear, and that are compatible with existing additive packages. Applicants"" invention addresses these needs.